I believe he is saying they are not mathematically accurate because values have to be interpolated from the look up table, most 3d luts are only 32 x 32 x32. So a lut can be mathematically acurrate if the color you are looking up matches one in the file otherwise it is going to be interpolated. However if your out size matches your bit depth then there would be be no interpolation.
It does not seem like much LUT support exists for SLog
- Thread starter Mike Krumlauf
- Start date
morgan_moore
Major Contributor
1024 * 3 = 3072 colours per 10bit pixel
4096 * 3 = 12288 colours per 12bit pixel
Possible colours to look up in a 32^3 LUT = 32768 possible colours
Seems big enough?
I might be all wrong.
4096 * 3 = 12288 colours per 12bit pixel
Possible colours to look up in a 32^3 LUT = 32768 possible colours
Seems big enough?
I might be all wrong.
morgan_moore
Major Contributor
You would appear to be correct 
As I said probably a different thread should happen as this is off topic to the OP.
As I said probably a different thread should happen as this is off topic to the OP.morgan_moore
Major Contributor
I started a seperate thead on LUTs in general. Sorry Mike if I thread jacked.
http://www.dvxuser.com/V6/showthrea...-about-LUTs-they-are-interpolators-TRUE-FALSE
http://www.dvxuser.com/V6/showthrea...-about-LUTs-they-are-interpolators-TRUE-FALSE
Mike Krumlauf
Award Winning Filmmaker
All good morgan, no worries
Cary Knoop
Veteran
A 1D LUT could do a one to one mapping, a full 3D LUT, where the RGB channels are dependent, can obviously not.
But perhaps you are missing the point of a colorspace transform, it's a mathematical formula that is not limited to a given source bit-depth and target bit resolution.
Colorspace transforms do a matrix transform by converting both the gamma and the gamut from a source to a destination colorspace (typically by converting to a linear light gamma and an XYZ gamut as an intermediate).
If you use professional color grading software there is no need to use LUTs for colorspace transformations.
But perhaps you are missing the point of a colorspace transform, it's a mathematical formula that is not limited to a given source bit-depth and target bit resolution.
Colorspace transforms do a matrix transform by converting both the gamma and the gamut from a source to a destination colorspace (typically by converting to a linear light gamma and an XYZ gamut as an intermediate).
If you use professional color grading software there is no need to use LUTs for colorspace transformations.
SJX
Veteran
Sorry my ignorance. But what is main difference? Seem to do the same? Luts also kind of transform?
Mike Krumlauf
Award Winning Filmmaker
Im not a math wizard by any means so I guess you could say Im a tad ignorant too on the subject. Never had a problem with LUTs when i've figured out a formula that looks right to me.... pretty bold to just say do away with them, even if its as a means to begin a manual grade yourself? Granted I did come from a world before LUTs so I get it, but then again back then I wasnt working with cameras that "needed it". DV was stuck in Rec709 lol
A 3d lut is basically a table of values like a spreadsheet. It takes an input color value and finds the new output color value from the lut and applys it, modifying the color.
A colorspace transform takes an input color and using equations and matrix math calculates the output color.
Since a lut is a table of values it generally doesn't have a output value for every input so the software will guess what the final color should be based of the nearby data in the lut file, this is the interpolation and normally software will offer different methods for doing so. A colorspace transform is a direct calculation so it is perfectly accurate for every possible input color and never interpolated.
You are not grading manually with a transform you could still convert to rec709 as you would with a lut, the only difference is the result is more accurate.
A colorspace transform takes an input color and using equations and matrix math calculates the output color.
Since a lut is a table of values it generally doesn't have a output value for every input so the software will guess what the final color should be based of the nearby data in the lut file, this is the interpolation and normally software will offer different methods for doing so. A colorspace transform is a direct calculation so it is perfectly accurate for every possible input color and never interpolated.
You are not grading manually with a transform you could still convert to rec709 as you would with a lut, the only difference is the result is more accurate.